Scientific errors in sf are not to be confused with Imaginary Science, where the author invents the science and tries to make it plausible, nor with Pseudoscience, where the author adheres to some alternative quasiscientific system unrecognized by the majority of the scientific community. Scientific errors are here taken to mean plain mistakes.

Sf in the days of the Pulp magazines was very much more prone to error than it is now, and it was for the absurdity of so much of the science, at least in part, that pulp sf (particularly in the 1930s) got a bad name; schoolteachers and parents were justifiably worried by its innumeracy as well as its illiteracy. Most sf written since the 1960s will pass scientific muster even with readers who have a little university-level science, but the excesses of the 1920s and 1930s must have been obvious even to many readers who had only a smattering of high-school science. Of course, some elementary errors can be hard to pick up. Hal Clement cites stories – notably William Golding's Lord of the Flies (1954) – in which myopic characters' spectacles are used to concentrate the Sun's rays and light a fire; Clement points out that these would in fact disperse the rays. By contrast, in The Tomorrow People (1960) Judith Merril used a helicopter for transport on the Moon, even though most schoolboys could have told her that it would not work without air.

Some errors are notorious. The fossil record and other considerations of evolutionary biology rule out the possibility of humans or near-humans naturally coexisting with dinosaurs, but the sheer attraction of the idea would often trump scientific plausibility, as in Charles G D Roberts's In the Morning of Time (coll of linked stories 1919) and many other early fictions. When Jules Verne uses a gun to shoot travellers at the Moon, he ignores the fact that the required acceleration would leave them as a thin red smear on the back wall of the cabin. The canali or channels which the astronomer Giovanni Schiaparelli (1835-1910) thought he saw on Mars were wrongly translated into English as "canals", and hence Edgar Rice Burroughs and many others felt justified in placing intelligent life there – a civilization based on waterways.

The history of pulp sf is full of examples of writers using Parsecs as a unit of velocity instead of distance, of confusing weight with mass (so that in space we have heroes able to push several tons of spaceship along with a tiny effort of one finger) and, most commonly of all, of exceeding the speed of light without any sort of justification (see Faster Than Light), as in A E van Vogt's "The Storm" (October 1943 Astounding): "Half a light year a minute; it would take a while to attain that speed, but – in eight hours they'd strike the storm." (The same story has a hero with a second brain which has an IQ of 917, as if somehow the exact figure might mean something.) Certain themes, such as Antigravity and Antimatter, have notoriously resulted in schoolboy howlers in much sf. In the pulp era Rockets would regularly perform manoeuvres, just like a car doing a U-turn. In fact, as most of us know in the space age, if you use gyros to turn a rocket it will continue in the same direction, unless another rocket blast is given in the new orientation to counter the original forward momentum. Nonetheless, Star Wars: Episode IV – A New Hope (1977), like many cinematic Space Operas since, has spacecraft taking part in what look like World War One dogfights. John W Campbell Jr, the man who was supposed to have done more than any other to put the science back in sf, was quite happy to publicize the so-called Dean Drive – in various editorials like "Report on the Dean Drive" (September 1960 Astounding/Analog), a proposed propulsion device which depends on violating the conservation of momentum: it pushes against itself. This is on a par with the "inertialess drive" which propelled E E "Doc" Smith's spaceships at fantastic velocity. Another favourite of the pulps was the electromagnetic spectrum, which was regularly rifled by writers in search of mysterious Rays which would have almost magical effects. Magnetism was yet another favourite, and all sorts of remarkably cock-eyed schemes were cooked up to exploit its hitherto unknown properties (though here we reach an area of overlap between straightforward scientific errors and such ingeniously plausible Imaginary Science as the theory of the Spindizzy). An especially enjoyable biological howler was the notion, common on pulp magazine covers, that Aliens would lust after human women, especially if partially unclad, this being on a par with men lusting after squids. Nevertheless, James Tiptree Jr made rather a good thing out of a similar notion in "And I Awoke and Found Me Here on the Cold Hill's Side" (March 1972 F&SF), the ultimate Exogamy story. And nearly all stories in the pulps about submicroscopic worlds (see Great and Small) used a model of the atom – seen as a kind of solid, spherical ball – which had been out of date for at least half a century by 1920. Ray Cummings, several of whose heroes shrink and have adventures on atoms, was a noteworthy offender.

Excesses of this kind still exist, of course, especially in the lowest echelons, but Robert A Heinlein and Isaac Asimov did much in the 1940s to bring scientific responsibility to sf, and their work was continued by Poul Anderson, James Blish, Hal Clement, Larry Niven and many others. If they committed errors, they mostly did so because they could not resist certain dramatic plot turns, like the end of Poul Anderson's Tau Zero (June-August 1967 Galaxy as "To Outlive Eternity"; exp 1970), where the crew of a spaceship survive to witness the ultimate collapse of the Universe into the monobloc – despite the fact that, in such a scenario, the whole of space would collapse: the very concept of being "outside" the monobloc is a contradiction in terms. Nevertheless, there are still novels being published which would not put the pulps to shame. Battlefield Earth (1982) by L Ron Hubbard was a classic example, containing such lunacies as invading Aliens who are said to come from another galaxy whose Periodic Table consists of Elements different from the ones we have here.

Sf in the Cinema and on Television, moreover, is often as scientifically illiterate as was pulp sf of the 1930s. Space: 1999 was a particularly bad offender. Bob Shaw has several times expressed amazement at the way that in the original Star Trek, when the Enterprise is buffeted about (as it frequently is), the crew are invariably thrown from their seats. Why, asks Shaw, in this supertechnological future, has the concept of seat-belts been forgotten? A particularly irritating error, almost invariable in film and television, is the audibility of explosions in space (as in Star Wars and Battlestar Galactica); it is apparently believed that, if the audience can't hear the bangs and whooshes, they'll all go home or change channels. Total Recall (1990) showed that things had not got much better, with at least two notable howlers. The first is the idea that, if you puncture a stationary pressurized dome, normal air pressure will be sufficient to produce hurricane winds that whip people and furniture out through the hole. (People can be sucked out of aeroplanes, but only because they are moving at several hundred miles per hour.) Even stranger was the notion that oxygen deprivation and near vacuum give people eyes the size of tangerines, a phenomenon they can sustain for some minutes without suffering damage. Monster Movies very often depend on giant ants, spiders, etc. In fact, such creatures could not exist unless radically re-proportioned; they would collapse under their own weight, not having legs, like the elephant's, designed to prop them up. Many problems arise with increases in scale, one of them being that the ratio between skin area and internal capacity does not stay the same, hence throwing the physiology of the body completely askew. Flying men are probably impossible, though Poul Anderson made a valiant attempt to rationalize them scientifically in War of the Wing-Men (1958; with restored text vt The Man Who Counts1978), greatly increasing their lung capacity and incorporating other necessary design changes.

Errors in sf are less common in the Soft Sciences, perhaps because these are subject to less rigorous laws, but nonetheless absurdities do occur. It is commonly supposed that, if we had Telepathy, we could understand Aliens bypassing language; however, there is strong evidence that we actually think in language, in which case Telepathy probably would not work efficiently between different nationalities, let alone between us and the Rigelians. Brainwashing, and mental conditioning generally, are in sf usually based on Pavlov's behavioural psychology rather than on B F Skinner's; that is, carried out through aversion and punishment, not through reward, even though the latter system has been amply demonstrated to be more efficient, and presents, perhaps, moral issues of a more subtle and interesting kind. [PN/JS]

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